At Kellogg’s Research Labs, we often make nitinol actuators for valve control. While valve actuators carry some similarities to all other kinds of actuators, there are some differences as well. This means that a little bit of study into those differences is warranted.
Nitinol valve actuators can be grossly classified as either passive or active.
Passive actuators: Passive actuators are exposed to the fluid of interest and actuate the valve based on the needs of the fluid. The energy required to power the passive actuators is derived from the heat of the fluid, so no external power source is required. Additionally, the passive actuator acts as a sensor and feedback loop all in one. As the temperature fluctuates throughout the region of interest, the stiffness of the passive actuator also fluctuates accordingly, allowing the valve to open and close as needed. By replacing a whole system of components, this usually results in a decrease in the cost to manufacture. At the same time, with little to no lag inherent to the system, the quality of output is increased.
Some examples of passive control valves are:
Mixing valves: When mixing fluids of different temperature, a passive nitinol actuator can control the valve position so that the output temperature is constant.
Control valves: When an engine is warming up, the ideal fuel/air ratio is different from when it is warming up. A passive nitinol actuator can be used to change the fuel and air flow in response to the engine temperature.
Active actuators: Active nitinol actuators act as a drop-in replacement for existing actuators.
Package size: Generally speaking, the benefit of using nitinol as compared to other actuation technologies is the reduction in package size. For one auto manufacturer, we replaced a 40mm long, 20mm diameter electric solenoid with a 2.4mm diameter, 16mm long actuator. Such tiny package sizes have allowed our customers to put valves into places that valves previously were not thought possible.
Steady State Power Reduction: Unlike electric solenoids, which must be fully powered at all times, a nitinol actuator can have the current reduced by up to 95% once steady-state is reached.
Cost Reduction: Reducing the cost of the actuator itself isn’t always possible. However, if you are replacing a whole system of components with a single nitinol actuator, cost reduction is almost always present.